1. Field of the Invention
The present invention relates to a control of an equalizer in a digital vestigial sideband (VSB) system, and more particularly, to a method and apparatus for controlling an equalizer using a sync signal in a digital VSB system, in which the sync signal is accurately separated even though a ghost having a short delay time and a large size is generated, and then the equalizer is controlled with the separated sync signal, to thereby improve system performance greatly.
2. Description of the Related Art
A digital broadcasting which provides video and audio information for multimedia services is being commercialized worldwide. In digital broadcasting, it is very crucial to provide a modulation and demodulation technique which can assume a sufficient bit transfer rate in order to transmit video and audio signals through a broadcasting channel having a predetermined bandwidth. An American-oriented ground wave digital broadcasting receiver is a digital VSB system employing a VSB modulation and demodulation technique in order to assume a high bit transfer rate in a limited bandwidth. A conventional digital VSB system is shown in FIGS. 1 and 2.
FIG. 1 is a block diagram showing a conventional digital VSB system. The digital VSB system shown in FIG. 1 includes a tuner/IF (Intermediate Frequency) unit 1 selecting a RF (Radio Frequency) broadcasting signal of a desired channel from an incoming signal via an antenna. The tuner/IF unit 1 converts a selected RF broadcasting signal into an IF signal and outputs the converted result. An analog-to-digital (A/D) converter 2 converts an IF analog broadcasting signal into a digital form according to predetermined frequency clock oscillating in a voltage controlled crystal oscillator (VCXO) 3 and outputs the digital signal. The output signal of the A/D converter 2 is input to a carrier recovery unit 5 formed of a digital frequency phase locked loop (DFPLL) and an automatic gain control (AGC) unit 8. The DFPLL 5 which is a carrier recovery unit corrects frequency and phase errors of the input signal by using a pilot carrier signal, and then demodulates the corrected result into a baseband signal to recover the carrier. The carrier recovered signal is input to a matched filter 6. The matched filter 6 corrects the carrier recovered signal of the DFPLL 5 into a signal equal to a passband predetermined in a transmission end, and removes noise other than the passband, to thereby play a role of heighten an accuracy of signals. The output signal of the matched filter 6 is input to a symbol timing recovery unit 4, an NTSC rejection filter (NRF) 7, the AGC unit 8 and a sync signal detector 10. The NRF 7 receives the output signal of the matched filter 6 and removes an NTSC component from the received signal, to thereby prevent degeneration of HDTV signals due to an analog NTSC TV signal. The sync signal detector 10 detects a data segment sync signal from the output signal of the matched filter 6, and outputs the detected data segment sync signal to the symbol timing recovery unit 4, the AGC unit 8, an equalizer 9 and other blocks.
Meanwhile, the symbol timing recovery unit 4 recovers a symbol timing error from the output signal of the matched filter 6 in synchronization with the data segment sync signal detected in the sync signal detector 10. Here, the VCXO 3 receives the output signal of the symbol timing recovery unit 4, generates timing recovered symbol clock, and provides the timing recovered symbol clock to the A/D converter 2 as sampling clock. The equalizer 9 equalizes the output signal of the NRF 7 in synchronization with the data segment sync signal detected in the sync signal detector 10, to thereby remove ghost and inter-symbol interference due to a multi-path occurring during transmission of ground wave broadcasting. In general, in the case of a digital communications system, a transmission end transmits a transmission signal in which a predetermined training sequence is inserted at every interval, and a reception end detects and recognizes the training sequence to thereby identify the pattern of the transmitted signal and perform equalizing. In the case that the transmission end cannot transmit the training sequence together with the transmission signal, the reception end cannot see the pattern and state of the received signal. In this case, a blind equalizing should be performed.
The output signal of the equalizer 9 is input to a phase tracker loop (PTL) 11. The PTL 11 attempts phase tracking in order to compensate for a phase error. The output signal of the PTL 11 is input a R-S (Reed-Solomon) decoder 14 via a TCM (Trellis coded modulation) decoder 12 and a deinterleaver 13 in turn. The R-S decoder 14 decodes an input signal according to the R-S decoding and corrects an error generated in a channel. That is, the R-S decoder 14 corrects an error using redundancy data in the case that an error occurs in original data. The error-corrected data in the R-S decoder 14 is input to a derandomizer 15. The derandomizer 15 reproduces a data packet for packet decoding from the input data. That is, a part of packets selected from the data packets are reproduced into an audio part of a digital broadcasting program and the other selected packets are reproduced into a video part of the digital broadcasting program.
FIG. 2 is a block diagram showing another conventional digital VSB system. The configuration of the digital VSB system shown in FIG. 2 is same as that of the FIG. 1 conventional digital VSB system. In FIG. 2, a frequency phase locked loop (FPLL) 51 is used as a carrier recovery unit instead of the DFPLL 5 of FIG. 1, and is positioned in front of an A/D converter 2.
The digital VSB system of FIG. 2 carrier-recovers the output signal of a tuner/IF unit 1 via the FPLL 51 in analog form and outputs the carrier recovered signal to an A/D converter 2. The A/D converter 2 samples the carrier recovered reception signal according to predetermined frequency clock oscillating in a VCXO 3 and converts the sampled result in digital form, to then output the digitally converted result to a matched filter 6 and an AGC unit 8. Since operations of the other components are same as those of FIG. 1, the detailed description thereof will be omitted.
By the way, since the conventional digital VSB systems perform symbol timing recovery using a data segment sync signal, and thus the systems normally operate after performing sync signal separation, an initial operation time is longer. Also, since sync signal separation is performed in front of an equalizer and thus a ghost having a short delay time and a large size is generated, it is not possible to separate and detect an accurate sync signal due to an influence of the ghost, which results in degeneration of the system performance.